1. Field of the Invention
The present invention relates to a mobile navigation system for displaying maps and displaying various routes on the displayed maps.
2. Description of the Related Art
FIG. 31 is a block diagram showing a conventional mobile navigation system disclosed in Japanese Patent Application Laid-Open No. 60-108709, for example. In the same drawing, reference numerals 21, 22, 23, 24, 25 and 26 respectively indicate a distance sensor, a bearing sensor, a signal processing device such as a CPU or the like, a running route storage device composed of one of various memories, a display and an operation device such as a keyboard or the like.
The operation of the mobile navigation system will now be described. Using the operation device 26, a user provides the present position of a vehicle on a map to the signal processing device 23 at the time of departure and sets a vehicle traveling direction on the map to a proper position. Each time the vehicle is driven by a predetermined distance (which is regarded as a distance X below) after the vehicle departs, position data is stored in its corresponding memory table provided within the running route storage device 24.
Four map display scales of 1 to 50000, 1 to 100000, 1 to 200000 and 1 to 400000 are available as display scales of maps displayed on the display 25. Memory tables corresponding to the display scales are provided within the running route storage device 24. The signal processing device 23 calculates position data, based on data outputted from the distance sensor 21 and the bearing sensor 22 whenever necessary. The calculated position data are respectively stored in the memory tables for the display scales of 1 to 50000, 1 to 100000, 1 to 200000 and 1 to 400000 each time the vehicle travels by distances 2.times., 4.times., 8.times. and 16.times..
FIG. 32 is a view for describing structures of memory tables. Reference numeral 31 indicates a memory table for storing position data corresponding to a display scale of 1 to 50000. Reference numerals 32, 33 and 34 respectively indicate memory tables for storing position data corresponding to display scales of 1 to 100000, 1 to 200000 and 1 to 400000 therein.
The signal processing device 23 reads position data corresponding to scales of maps displayed on the display 25 from the memory tables 31 through 34 and supplies the read position data to the display 25. When the map is displayed on the scale of 1 to 200000, for example, the display 25 displays, as vehicle travel loci, data set on every distance 8.times., which have been read from the memory table 33. When the map is displayed on the scale of 1 to 100000, the display 25 displays, as vehicle travel loci, data set on every distance 4.times., which have been read from the memory table 32. Further, when the map is displayed on the scale of 1 to 50000, the display 25 displays, as vehicle travel loci, data set on every distance 2.times., which have been read from the memory table 31. Thus, even when the map is displayed on any display scale, the vehicle travel loci are displayed on the display screen at equal intervals.
The conventional mobile navigation system is constructed as described above. Further, the distances traveled by the vehicle are calculated and the vehicle travel loci are displayed for each of the distances corresponding to the respective map scales. However, this method can be applied to the case where the loci are displayed after the vehicle has been driven. However, when a route such as a route to be recommended along which the vehicle is not yet driven, is displayed, such a conventional method cannot be used.